At first glance, the swearing in of a new Congress today marks a concentration of power for George W. Bush that is nearly without precedent in the post-World War II period.

For the first time since 1954, a Republican president is matched with a Republican-majority House and Senate - a Congress his campaigning helped create.

But Mr. Bush, while holding the political high ground, will not find a rubber stamp at the end of every gavel on Capitol Hill.

He clearly wants and expects to set the agenda on everything from Arctic oil drilling to prescription drug benefits. Today, he unveils a major new tax-cutting plan to stimulate the economy.

Yet both Houses of Congress remain only narrowly under Republican control. Democrats are sure to find ways to parry White House goals, whether by Senate filibusters or peeling some Republicans to their side on key votes.

And, while GOP leaders in general are closely allied with Bush, Republicans themselves could prove nettlesome to the Bush agenda. In the Senate, many incoming GOP committee chairmen are lining up agenda items that are off - or even at odds with - Bush's wish list.

Tomorrow, for example, Sen. John McCain (R) of Arizona plans to chair hearings on a sweeping proposal to address global warming by mandating reductions in US greenhouse-gas emissions, something the White House opposes.

Indeed, a hallmark of the Senate is to resist taking direction either from House colleagues or the White House.

Senate Democrats, for their part, are regrouping after midterm losses that surprised many here. Sens. John Kerry of Massachusetts and John Edwards of North Carolina have already announced bids for the presidency in 2004, with several others likely to join them.

The Senate of the 108th Congress is even more than usually in flux. It convenes with a heavy load of unfinished legislative business, including 9 of 11 spending bills for a fiscal year that is now into its second quarter. Nor has the outgoing Senate leadership resolved how to reorganize committees and staff, after a historic power-sharing agreement ran out at the end of the last Congress. Until they do, Democrats will continue to control committees.